The Applicant has already filed provisional application number 60/914,658 on Apr. 27, 2007 to a laser plasma spectroscopy system, which is now incorporated by reference in U.S. application Ser. No. 12/597,761. The examples disclosed in these applications stimulate plasma to enhance a detected signal at a stand-off distance from which chemicals at or near a surface may be sampled. The disclosures of these applications are hereby incorporated by reference in their entirety.
A key design parameter of a RAMAN spectroscope is the wavelength'of the laser, which is typically optimized for specific conditions and for a particular application. In U.S. Pat. Publ. No. 2011/0013267, published Jan. 20, 2011, and filed Jul. 17, 2009, a RAMAN pump light source is activated at a plurality of pump wavelengths and power levels such that only one pump wavelength is active at any given pump power level, achieving amplification gain in an optical fiber probe by backward propagation amplification. This technique is useful for configuring a RAMAN distributed amplifier for optical network equipment. However, RAMAN interaction may cause deleterious effects, including RAMAN scattering, crosstalk, non linear distortions, increased noise levels, distortion, unacceptable carrier to noise ratios and attenuation. See U.S. Pat. Publ. No. 2010/0316382, which published Dec. 16, 2010 and was filed Jul. 11, 2009, which discloses a method of back-pumped distributed RAMAN amplification using an unmodulated laser of an appropriate wavelength at the distal end of a fiber far from the opposite end where co-propagating signals are launched.
U.S. Pat. No. 6,996,135 discloses a cascaded RAMAN laser with wavelength selectors and an intercavity section that is made of a non-linear optical medium, resulting in multi-wave mixing amplification, transferring energy from radiation with shorter wavelengths to radiation with longer wavelengths more efficiently.
U.S. Publ. No. 2009/0137544, published May 28, 2009 and Dec. 10, 2007, claimed priority to several provisional applications and disclosed a multimodal multiplex multi-wavelength RAMAN spectroscopy system for high through-put fluorescence for detecting alcohol in tissue and cholesterol testing in Zebra fish embryos. The sensor included a combination of spatially coded detecting optics and spectrally coded excitation sources to get a RAMAN spectrum of alcohol in tissue, from 1600 to 1000 cm−1.
U.S. Pat. No. 4,680,745 issued Jul. 14, 1987 and disclosed an optical system using variable beam expanders and other optical elements for recording pits and grooves on a surface of a recording medium. Light having different wavelengths for the pits and grooves was disclosed.
A five-wavelength LiDAR system was used by the Centre for Atmospheric Science at the University of Manchester, which was designed by Flight lasers of Germany using a Continuum PL8020 Nd:YAG laser in conjunction with a multiplexer to pump Raman shifting cells to produce wavelengths of 266, 289, 299, 316 or 315 nanometers. Wavelengths of 289, 299 and 316 nanometers are generated by stimulated Raman scattering in three respective Raman cells. The system uses the five wavelength beams to measure attenuation and to calculate the vertical distribution of ozone and aerosols in the atmosphere.
U.S. Pat. No. 4,870,275 issued Sep. 26, 1989 and disclosed remote detection of gases in the atmosphere using a Raman-shifted excimer/dye laser beam through a circulating-medium Raman-shifting cell, allowing an infinite number of different wavelengths of emitted radiation for measurement. Wavelengths are emitted in absorbed and non-absorbed ranges to calculate the presence and quantity of gases in the atmosphere. U.S. Pat. No. 7,583,264 issued Sep. 1, 2009 and disclosed an eye-safe atmospheric aerosol LIDAR using a stimulated Raman scattering gas cell and non-focused laser beam geometry. U.S. Pat. No. 7,869,469 issued Jan. 11, 2011 and discloses a Raman shifter with improved optical efficiency and robustness including a source system having a source pump laser and a seed laser, which are combined for transmission into a Raman cell having a multi-pass pathway through the cell using a medium that is circulated in a direction transverse to the beam pathways. U.S. Pat. No. 8,009,288 issued Aug. 30, 2011 and disclosed a system containing a stimulated Raman or coherent anti-Stokes Raman spectroscopy system using a resonant cavity containing a sample of a nucleic acid derivative in solution for analysis and sequencing of the nucleic acid.
U.S. Publ. No. 2006/0092995 published May 4, 2006 and discloses a multi-wavelength, commonly mode-locked external cavity laser system. A wavelength-selective device controllably transmits or reflects diffracted optical beams depending on the wavelength. U.S. Publ. No. 2007/0146506 published on Jun. 28, 2007 and disclosed a system for determining the vignetting function of an image and using the function to correct for vignetting if present.
U.S. Publ. No. 2009/0237648 published Sep. 24, 2009 and discloses a system for performing Raman spectrometry mounted on a vehicle using dual pulsed beams at a first wavelength and a second wavelength to identify a target by matching a Raman signature with a given collected Raman spectra. The system is used for detecting chemical or biological agents under a vehicle or at a short distance (e.g. up to 1.5 meters). According to the reference, 1.5 meters is considered a “standoff range.” To be considered a “stand off distance” in this application, a system must be able to identify a target at a distance up to and including forty (40) meters. A system having a range for identifying a target less than 40 meters is not considered as operating at a stand off distance, notwithstanding the suggestion in U.S. Publ. No. 2009/0237648, which teaches that there is still a need for improvements in stand-off on-the-move detection systems. Applicant agrees that there is still a need for improvement but disagrees that a range up to 1.5 meters provides for stand off detection as that term is defined herein.
U.S. Publ. No. 2012/0099102 published Apr. 26, 2012 and discloses probes for focusing outputs from a plurality of light sources or lasers onto a sample and collecting backscattered radiation from the sample, separating Raman spectra from backscattered light and providing at least on output containing the Raman spectra. This publication teaches that fiber optic Raman probes offer favorable configurations, but teaches that there is a need for increased efficiency, accuracy and accessibility in Raman measurements, such as to avoid interference from luminescence or fluorescence bands, to provide spectra in regions where detectors having their maximum response and to provide probes that are compact or handheld. The disclosed device enables a Raman spectra of two or more excitation wavelengths to be obtained simultaneously. As an example, the publication discloses two excitation laser sources and one or more spectrographs receiving Raman signals via one or more fiber optic channels.
None of the sensors, amplifiers or detectors of the known references disclose, teach or suggest a multi-wavelength laser capable of use in RAMAN spectroscopy suitable for use at stand off distances and/or using a laser capable for use as a component of a system capable of being used for neutralization of a threat.